1. Field of the Invention
This invention relates to a recording medium in which data can be recorded in terms of headers, main data and sub-data as plural unit blocks and in which the recording capacity for the sub-data can be varied without decreasing the recording capacity of the main data. This invention also relates to a reproducing apparatus for reproducing the recording medium.
2. Description of the Related Art
In a conventional recording medium, there is provided, separate from a region for recording main data signals, a recording region for sub-data signals read out simultaneously with the main data signals. These sub-data signals, also termed sub-data or sub-codes, are used for recording the ancillary information, such as graphics information or text data.
In a compact disc (CD, registered trade mark), for example, there is provided, separate from the region for recording audio signal data, a region for recording sub-data that can be reproduced simultaneously as the audio signals are reproduced. These sub-data include letters, graphics, etc in addition to the information such as the numbers of musical numbers, indexes or playing time. In CD-G (CD-graphics), for example, the graphics information is recorded in six bits termed user bits of the sub-data so that a picture or a lyric is displayed simultaneously with the accompaniment (karaoke).
Meanwhile, since the data transfer speed of sub-data is of the order of several kBps, such as 5.4 kBps (kilobyte per second), the graphics information that can be recorded as sub-data cannot be expected to be of a high quality. This is far below the 64 kBps required for so-called streaming reproduction on the Internet now in popular use world-wide. Insofar as the still picture is concerned, the data transfer rate for displaying the high-quality still picture, encoded by the JPEG (Joint Photographic Experts Group) format or the GIF (graphics interchange format) now in popular use, cannot be met.
In order to cope with the streaming reproduction or high-quality still picture, a high transfer rate exceeding 64 kBps for ancillary data is required. However, for realizing the high transfer rate, it is necessary to provide a region for a large amount of the ancillary information needs, as a result of which the main data region is decreased. If the main data region is decreased, the net result is the decreased music reproducing time or the lowered sound quality.